Effect of mucosal removal on the response of the feline bladder to pharmacological stimulation

The urothelium plays an important role in the maintenance of normal bladder function. It provides a nonpermeable barrier to the contents of urine. The urothelium is directly involved in the transduction of both intravesical pressure and intravesical volume information to the afferent nerve fibers located within the lamina propria area. A third function may be to modulate bladder contractile function through local secretion of bioactive substances into the muscularis layers adjacent to the urothelium. To test this last hypothesis, the following experiments were performed: Strips of female cat bladders were isolated from the bladder body, base and urethra. The mucosa of alternate adjacent strips was removed, and the contractile response to field stimulation (FS), bethanechol (body), phenylephrine (base, urethra) and KCI was determined. For the bladder body, the strips without mucosa responded to FS, bethanechol, adenosine triphosphate (ATP) and KCI significantly greater than the strips with mucosa intact. For the bladder base and urethra, the contractile responses to FS, KCI and phenylephrine were significantly greater for the strips with mucosa removed as compared with the strips with mucosa intact. For the urethra and bladder base, FS in the presence of phenylephrine produced a relaxation. For the bladder base, the degree of FS relaxation of the isolated strips with mucosa removed was significantly greater than the strips with mucosa intact. For the urethra, FS relaxation was similar for the two groups. In conclusion, removal of the urothelium significantly and substantially increased the contractile response to FS, KCI, bethanechol and phenylephrine. Field stimulation relaxation in the bladder base was also enhanced. Thus in the cat, the mucosa has a significant inhibitory effect on the contractile response of the bladder to stimulation. The mechanism of this activity is not clear at the present time but will be the subject of further study.